1. Field of Invention
This invention relates, in general, to an apparatus for registering workpieces on a computer controlled drilling machine and, in particular, to registration apparatus which allows a drilling machine to automatically position registration pins to accommodate workpieces of various sizes. The invention relates especially to a registration pin mechanism wherein the registration pin may be precisely positioned along a line of position under the control of the drilling machine.
2. Prior Art
The drilling operations performed in conjunction with manufacturing printed circuit boards or panels are required to be performed to very precise tolerances. The drilled holes are commonly of a diameter of 0.0018 of an inch or less and typically must be positioned within a tolerance of 0.00017 inches or less. These drilling operations are performed with a computer controlled drilling machine under automatic numerical control and may typically involve thousands of drilling operations per panel. The printed circuit board panels are placed on a horizontal work platform or tooling plate located below the drill spindle. The panels are typically stacked up to three or four high on the tooling plate of the drilling machine so that several panels are drilled at the same time. Often drilling machines have several spindles so that there may be several stacks of panels drilled on the same machine. Since the spindle must be able to reach any point on the panels, relative movement in three dimensions is required between the spindle and the panels. This requirement has been implemented in various ways. In a common drilling machine design, the tooling plate moves in one horizontal dimension and the drill spindle moves in the orthogonal horizontal dimension and also in the vertical dimension.
In order for the numerically controlled drilling machine to hole the required drill pattern in a panel, the panel must be registered to the coordinate system of the drilling machine. A common method of registration is to position the center of the panel in the same place on the tooling plate of the drilling machine regardless of the size of the panel. Under this registration system, the panels are provided with four slots that fit over four upright pins disposed on the tooling plate of the drilling machine. A first pair of slots is located on a first centerline of the panel, usually near the opposing edges of the panel with the longer axis of each slot located on the centerline. The second pair of slots is located on the centerline orthogonal to the first centerline near the other opposing edges of the panel, again with the longer axes of the slots located on the orthogonal centerline. The corresponding upright pins on the tooling plate are located to position the center of the panel at the prescribed location in the coordinate system of the drilling machine. Under this registration system, the two slots positioned on the same center line and the associated registration pins, contain the position of the panel in the dimension orthogonal to the centerline upon which they are disposed. Correspondingly, the other two slots and associated registration pins position the panel in the other dimension. Accordingly when the panel is placed over this set of four pins, its position is determined with respect to the coordinate system of the drill.
For many years the panels have been hand loaded onto the tooling plate of the drilling machine. Because the registration pins were required be located in numerous places on the tooling plate to accommodate different size workpieces and different registration systems, the tooling plate was provided with removable plugs in the general area where the registration pins were to be located. The drilling machine itself was then used to drill precisely positioned registration holes in the plugs and the registration pins were manually inserted in the holes. When a panel that required a different location of the registration pins was to be drilled, the registration pins were manually repositioned to new holes in the removable plugs which were appropriately located for the dimensions and design of the new panel. This approach is very accurate because it uses the coordinate system of the drilling machine to drill the new registration holes in the appropriate locations, but it is time consuming, requires the drilling of new holes for the registration pins and the manual insertion of the pins, and often requires a complete setup operation including installing new plugs.
Another method has been to install registration pins permanently in a single registration pattern on the tooling plate and require that the panels be separately registered on carriers which would then be placed on the drilling machine. This requires a new carrier for each size of panel. Furthermore, because two registrations are in fact required--one for the carrier on the tooling plate and one for the printed circuit board panel on the carrier--two sets of potential registration errors are also produced.
Recent trends in flexible manufacturing have created a need to reduce the time and operator demands of the registration process. Also batch sizes have been getting smaller and are predicted to get still smaller in the future. Consequently, a manufacturer is required to be flexible enough to handle these small batch sizes and the resulting frequent setup operations. The necessity to accommodate workpieces of various sizes and various locations of the registration pins has required that the pins be positionable precisely over a continuous range of possible locations. And finally, with the advent of apparatus for automatically loading the panels on the drilling machine, the registration process is the only remaining operator intensive function in the computer controlled drilling process.